Method for structured energy transmission using electron beams

ABSTRACT

Multiple methods are known to process materials or alter their properties using an electron beam. Until now, it was not possible to impinge upon minuscule surface sections (pixel) with a given arrangement on the surface in order to achieve certain effects. According to the invention, the object to be impinged upon is moved contact-free under a mask. A bidimensional deflectable electron beam oscillating at a high frequency perpendicular to the direction of movement of the object is moved on the mask, the speed being essentially faster than that of the movement of the object. Said method can be used for processing any material, preferably plane or band-shaped objects, in order to achieve processing effects by means of physical or chemical reaction.

The present invention relates to a method for structured energytransmission by transmitting for short periods energy using electronbeams to limited surface elements of, preferably, plane surfaces ofobjects—such as parts, plates or bands of metallic, semi-conductive ordielectric materials or combinations of such. The useful processingeffects are determined by the physical or chemical reactions of thematerials to the energy transmission by means of electron beams. Thepreferred field of application is the structuring of surfaces onstrip-shaped objects of any length by means of a limited number ofrepeated structural elements which are matrix-like arranged in columnsand lines.

It is general knowledge how to use electron beams in a large variety ofways to respectively process materials or change material properties. Inthe main, probe- and mask-type processes are applied to generate surfacestructures.

Probe methods are characterised by the application of a focused electronbeam which, according to the structural elements to be generated,affects the object by programmed beam deflection, which is known per se.With this method energy is transmitted to the different surface spots ina certain time sequence. The application of this method isextraordinarily flexible. However, its disadvantage is that it cannotgenerate structural elements whose lateral expansion is smaller than thediameter of the electron beam focal spot. Frequently, it is also notpossible to place too high demands to the homogeneity of the energydensity to be transmitted per surface unit within the structuralelements. Although this method allows for a homogeneity improvement byreducing the focal point diameter via the modification of theoptoelectronic focusing conditions, the adverse consequence is areduction of the usable beam deflection amplitude. Then larger surfacesare processed by means of time-consuming mechanical shifting of theobject, e.g. with the step-and-repeat technique. One limitation of theapplication of the probe method is particularly the structuring of largesurfaces with densely located small structural elements, where thetechnically limited beam deflection velocity of the electron beam isable to extend the processing duration for a certain task till well intothe range of the inefficiency of the processing method. In addition,when thermal processing effects are used, the probe method is often notable to meet the demand for a sufficient simultaneity of energytransmission to the entire structural element.

The structured energy transmission according to the mask method appliesdifferent task-specific variants—predominantly in electron beamlithography, where the optoelectronic imaging of a template, whichilluminates the structural elements as recesses by the electron beam,has gained a certain significance. Combination techniques are alsoknown, characterised by the optoelectronic imaging of a template whichcontains the structural elements and the latter's positioning on theobject as defined by an additional beam deflection. The disadvantages ofthese techniques are their high apparatus requirements and the lowvalues of the momentarily transmittable energy density. Hence, theirpractical application is restricted to electron beam lithography for thegeneration of latent structures in the micron and sub-micron range.

The invention is based on the task of developing a method for structuredenergy transmission to an object surface by means of electron beamswhich gets past the limitations of the prior art methods. Thus it shallbe possible to impinge upon minuscule surface sections, e.g. pixels,using an electron beam with a given arrangement on the surface in orderto achieve certain processing effects. In particular, it shall permit adefined variability of the transmitted energy density for a limitednumber of different structural elements. Non-thermal and thermalprocessing effects shall be achievable with a high productivity and ahigh quality.

According to the invention the task is solved according to thedefinitions of patent claim. Further advantageous embodiments aredescribed in patent claims 2 to 11.

Essentially, the solution according to the invention is provided in thatan electron beam is high-frequency deflected in the known way into onedirection—the oscillation direction—according to a periodic functionand, nearly perpendicular to the oscillation direction—in deflectiondirection -, is made to act using beam deflection via the recesses in amask onto the surface of an object which is moved contact-free under themask in the oscillation direction. The motion speed of the electron beamin the deflection direction is high compared to the speed of movement ofthe object. The energy is transmitted to the object surface sections,which are defined by the lateral expansion of the mask recesses, inseveral partial amounts that are determined by the frequency of theperiodic deflection function, the speed of the beam deflection in thedeflection direction, the beam diameter in the mask plane and thelateral expansion of the mask recesses. If there is a high demand to thehomogeneity of the energy density the three first-mentioned influencingvariables shall be matched. Most application require a constant energydensity in at least one structural element, in which case it is suitableto use a known trigonometric function for the periodic beam deflection.

When carrying out thermal processing methods it is necessary to transmitthe required energy density within a short period of time in order toachieve a quasi-adiabatic energy transmission, i.e. without anyessential heat dissipation from the energy-absorbing material volumeduring the energy transmission period. Particularly in this case theelectron beam is focused into the mask plane and the periodic deflectionkept as high as technically possible, e.g. in the range between 100 kHzand 1000 kHz. The beam deflection speed into the deflection direction israted sufficiently high so that the energy transmission period, whichresults from the ratio between the beam diameter in the mask plane andthe beam deflection speed, meets the demands to a sufficient adiabaticbeam deflection speed. The impact on the processing effect of the exacttransmission of the periodic deflection function, which is hardlyimplementable in this case, is limited in the mirror points by choosingthe amplitude larger by a number of beam diameters than the width of therecess sections in the mask.

If the structuring of an object requires energy densities that slightlyvary locally, their adapted selection is suitably made by choosing anappropriate amplitude of the periodic deflection function.

If the structural elements are arranged matrix-like on the object, it issuitable to choose the two deflection directions nearly perpendicularlyto each other according to the structural arrangement on the object.

If all structural elements shall be impinged with about the same energydensity it is suitable to keep the beam deflection speed constant in themask deflection direction. While in case of a high variation of theenergy density it may advantageous to perform the matching by means of aposition-depending deflection speed into the deflection direction.

During thermal processing methods the thermal loadability of the maskmay limit the method. In such case it is advantageous to manufacture themask of material with good heat-conducting and temperature-resistantproperties and to design a water cooling system directly adjacent to therecess section. Here, the mask recesses are restricted to a gap. Theparallel arrangement of a number of such gaps in the mask, through whichthe electron beam travels cyclically one after the other, canconsiderably increase the thermal loadability of the mask. Sucharrangement of gaps in the mask can also be advantageous when structuralelements, which are located on the object closely to each other in thedirection of the gap, shall be impinged with differing energy densities.

In order to achieve a high process productivity it is advantageous tomove the object to be processed under the mask perpendicularly to thedeflection direction and at a constant speed. High demands to therectangularity of the processing structure on the object can be metunder these conditions by turning the mask towards the structure on theobject—at constant beam deflection speed into the deflectiondirection—in such a way that the impact of the operating time effect onthe position of the surface elements on the object which are impinged bythe electron beam is eliminated by the finite beam deflection speed intothe deflection direction.

The process according to the invention can be particularlyadvantageously applied when strip- or band-shaped objects, whose widthis within the implementable beam deflection amplitude in the deflectiondirection, shall be processed in a structured way. In case that theobject width exceeds these limits it is possible to impinge the entireobject surface by combining strip-shaped partial surfaces.

One advantageous application area is the highly efficient structuredprocessing of objects with a relatively large surface. In the sphere ofnon-thermal electron beam processing this applies predominantly to thestructured modification of plastic materials, the creation of colourpatterns in materials filled with suited electron-beam-sensitive dyes.

In the sphere of thermal electron beam processing the process can beapplied both in the optical structuring of suitably sensitised glasssurfaces in order to generate displays and in the structured hardeningof metal surfaces from hardenable materials or for abrasive processing,e.g. of plastics by means of material evaporation.

The preferred area of application of the process are plane strip- orband-shaped objects, although also curved surface can be processed, e.g.cylindrical objects, where, if need be, the mask shall be matched to theobject shape.

In the following an embodiment of the invention is described in moredetail with reference to the appended drawing, where

FIG. 1: is an illustration of an object to be processed with therequired means,

FIG. 2: is an illustration of a surface element in an enlargedrepresentation (Trimmed area A).

A 10-cm wide strip-shaped glass substrate 1 with a specially preparedthin surface layer 2 shall be structured by electron beam processing ina surface structure consisting of pixels 3 that are arranged in asquare, orthogonal matrix, with four pixels 3 (3.1 to 3.4) each formingone colour element 4. In order to achieve the desired optical effect thefour pixels 3 shall be impinged upon with slightly differing energydensities. This processing effect is a thermal effect which requires thepixel 3 sections of the thin prepared surface layer 2 to travel throughtemperature cycles with the same duration but slightly differingtemperatures so as to obtain certain optical properties in eachindividual pixel.

The process according to the invention is implemented as described inthe following: The substrate 1 is placed on a common table 5 which movesin the x-axis. The table 5 is moved in the x-axis at a constant speed.The table drive, which is not shown, is connected to a known measuringsystem which defines the exact momentary movement co-ordinate in the xdirection. The stationary mask 6 (only partially shown) is locateddirectly above the substrate 1, but without contact to the latter. Themask contains the recesses 8; 8′ along the gaps 7 and 7′ through whichthe electron beam 9 is made to impact the pixels 3 on the substrate 1.The pixels 3 per each colour element 4 are impinged upon with slightlydiffering energy densities. The electron beam 9, with its appropriatelystabilised parameters: accelerating voltage, beam current and beamdiameter in the mask plane 6, initially impinges upon an intensivelymask 6 area outside of the recesses 8. The electron beam 9 is deflectedinto the direction indicated by the arrow 10 (oscillation direction)parallel to the x direction and oscillating symmetrically to the axis ofgaps 7; 7′ according to a periodic delta function with 200 kHz.

The deflection amplitude is selected approx. five beam diameters largerthan the expansion of the pixels 3. Thus the impact of the finitethreshold frequency on the homogeneity of the energy density transmittedto the substrate 2 is sufficiently eliminated. Accelerating voltage,beam current, amplitude of periodic deflection and the preselecteddeflection speed are matched in such a manner that the required energydensity can be transmitted in the pixels 3. Upon pixel 3.1 achievingcongruence with the top recess 8 in gap 7 of the mask 6 the electronbeam 9 is led with the appropriate speed across the entire substratewidth in y direction. The electron beam 9 retracted across the cooledsection of the mask 6 along the direction indicated by the arrow 11 intothe second initial position indicated by the arrow 10′ where, first, theamplitude of the periodic deflection function is matched to the requiredvalue of the necessary energy density. Upon the next pixels 3.2achieving congruence with the next recess 8′ in gap 7′ of the mask 6 theelectron beam 9 is led with the same deflection speed as before acrossthe gap 7′ of the recess 8′ of the mask 6. The retracting of the beam onthe mask 6 is made along the same route as indicated by the arrow 11back into the position of the arrow 10. Now, following the previousamplitude matching of the periodic deflection function, the energytransmission is carried out analogously and, thus, the processing of thenext pixels 3.3 and 3.4. The x distance of the axes of the gaps 7; 7′,the operating period of the electron beam 9 across the substrate widthand the adjusting times for the different periodic deflection amplitudesof the electron beam 9 are suitably matched in order to appropriatelyposition the pixels 3 on the substrate 1. During the processing sequencecolour elements 4 are generated which are matrix-like distributed acrossthe entire surface of the object 1. Said colour elements 4 each consistof four pixels. As a result of the above-described processing steps thepixels 3.1-3.2-3.3-3.4 below the recesses 8 or 8′ of the mask 6 areimpinged upon by the electron beam 9 one after another and in quicksuccession. The energy intake of the electron beam 9 which changesduring each pass of the electron beam 9, i.e. the energy intake ismatched to the desired result, different optical properties are obtainedfor each pixel 3 in a given colour element 4. The energy densityrequired for the above-described method is several Wsec/cm². An electronbeam 9 with a radiant power of a few kW yields a typical deflectionspeed of >20 m/sec. At a substrate width of 10 cm the operating time ofthe electron beam 9 across the substrate is approx. 5 msec. A furthermax. 5 msec are necessary for retracting the beam and matching theamplitude. Hence, the processing time for one gap of structural elementsis 10 msec, which means that 100 gaps can be processed per second. At ax distance of the gaps 7; 7′ of the pixels 3 of 0.2 mm the requiredtable motion speed is 2 cm/sec. Then the structured surface per secondis 20 cm². The ratio between the table speed and the deflection speed ofthe electron beam 9 of 1. 1000 results in a corresponding deviation fromthe orthogonality between the rows and columns of pixel 3. If saiddeviation is unwanted it can be eliminated by a corresponding turning ofthe mask 6 in counter-clockwise direction.

The relatively high thermal load of the mask 6 requires its intensivecooling, which is provided by water cooling ducts 12 in the mask 6.

What is claimed is:
 1. A method for the structured energy transmissionusing electron beams onto a glass substrate having a specially preparedsurface layer by means of a focusable, bidimensionally deflectableelectron beam comprising the steps of: (a) moving the substrate under amask having recesses without contact with said mask; and (b) moving theelectron beam in the direction of movement of the substrate, saidelectron beam oscillating at a high frequency approximatelyperpendicular to the direction of movement of the substrate across therecesses present in the mask, so that the substrate is acted uponthrough each recess by the electron beam; and (c) coordinating aplurality of electron beam parameters with each other so as to form onthe surface layer color elements comprising a plurality of pixels ofvarying color, the color of each pixel varying with the change in energytransmitted to the pixel, said parameters comprising accelerationvoltage, beam current, periodic deflection amplitude and deflectionspeed.
 2. The method of claim 1 further comprising the step ofdeflecting the electron beam in the direction of oscillation of theelectron beam in accordance with a trigonometric function wherein anadiabatic introduction of energy takes place when a high surface energydensity is transmitted so that each pixel to which said energy isintroduced is not influenced thermally by neighboring pixels.
 3. Themethod of claim 1 further comprising the step of deflecting the electronbeam in the direction of oscillation of the electron beam in accordancewith a periodic deflection function in which the beam deflection speedinto the direction of movement of the substrate is sufficiently high sothat the amounts of energy transmitted to the surface layer have aselected level of homogeneity.
 4. The method of claim 3 wherein theamplitude of the periodic deflection function is selected to be higherthan the expansion of the recesses in the mask located in theoscillation direction.
 5. The method of claim 3 wherein the energydensity to be transmitted at constant beam current is matched bychanging the amplitude of the periodic deflection function.
 6. Themethod of claim 1 wherein the speed for the deflection of the electronbeam to its oscillation in vertical direction can be kept constantacross the entire section of recesses in the mask.
 7. The method ofclaim 1 wherein the speed of the electron beam deflection in orthogonaldirection of the direction of the movement of the object is selected sohigh that the energy transmission to the pixels to be impinged upon iscarried out without essential heat dissipation from the energy-absorbingmaterial volume during the energy transmission period.
 8. The method ofclaim 1 wherein the electron beam is position-dependent deflected at avariable speed to achieve a local variation of the energy density to betransmitted to the substrate.
 9. The method of claim 1 wherein the maskis cooled.
 10. The method of claim 1 wherein the substrate to beprocessed is moved under the mask at a constant speed.
 11. The method ofclaim 1 wherein, according to the beam deflection speed perpendicular tothe oscillation direction and the speed of the movement of thesubstrate, the mask is turned towards the y direction in such a mannerthat the operating time effect of the electron beam across the mask iseliminated regarding the co-ordinate position of the pixels which areimpinged upon.